Chemical communication is the primary means of communication with others of the same species in most mammals. Even humans show a significant, if largely subliminal, form of chemosensory communication, as when women living together influence each others' menstrual cycle. The amygdala is a primary brain area involved in evaluating sensory/social information of all kinds, in rodents and in humans. It is involved in the recognition and categorization of facial expression in humans, a process that is deficient in autism spectrum disorder and related conditions. The medial amygdala is particularly important in processing and categorizing information about unlearned chemosensory signals. We and others have identified circuits in medial amygdala of different animal models that distinguish categories of chemosensory information and these circuits share critical features with circuits used by other amygdala divisions analyzing other sensory signals in a variety of species. Here we investigate the activation of these circuits, in behaving animals at the cellular level in the brain, to test alternative hypotheses about the principles of operation of amygdala circuits in discriminating unlearned pheromone-like chemosignals. The amygdala is also involved in reassigning value to chemosensory stimuli based on experience, Here we will modify the meaning of chemosensory stimuli in behaving animals, by conditioning and determine whether information is re-routed to engage a new output circuit, and whether categorization seen with unconditioned stimuli is maintained, altered or absent. Immediate-early gene expression will be used to map brain responses at the cellular level (averaged over time) and single-neuron electrophysiology will be used to measure responses to multiple stimuli (at higher temporal resolution), in order to identify and characterize the neurons involved. The functional connections between sets of neurons within the circuit will be determined by anatomical tracing of neural connections. The function of the amygdala in sensory processing and in reassigning salience to sensory stimuli as a result of experience will be investigated in this study. These processes may be involved in autism or other disorders of sensory evaluation, affect and communication. Relevance the research investigates the operation of circuits within the amygdala, a region in the mammalian brain implicated in autism spectrum disorder and related conditions. The rodent amygdala uses circuits to analyze and classify chemosensory signals that have common features with circuits used by other species to analyze and classify other types of sensory stimuli. [unreadable] [unreadable] [unreadable]